Re: [Qemu-devel] [PATCH] linux-user: Add missing check for return value of lock_user

[Peter Maydell <peter.maydell@linaro.org>]

On 14 March 2015 at 15:12, Stefan Weil <sw@weilnetz.de> wrote:
> This fixes a warning from Coverity:
> "Dereference null return value (NULL_RETURNS)"
>
> Signed-off-by: Stefan Weil <sw@weilnetz.de>
> ---
>  linux-user/flatload.c |    8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/linux-user/flatload.c b/linux-user/flatload.c
> index 566a7a8..56ac790 100644
> --- a/linux-user/flatload.c
> +++ b/linux-user/flatload.c
> @@ -97,11 +97,13 @@ static int target_pread(int fd, abi_ulong ptr, abi_ulong len,
>                          abi_ulong offset)
>  {
>      void *buf;
> -    int ret;
> +    int ret = -TARGET_EFAULT;

The return value for this function should be a host errno,
not a target errno, I think. (If you track back upwards
then eventually main.c calls loader_exec() and treats the
return value as a host errno.) This seems like the right
thing given that these loader functions are all pre-run
setup, and are not involved in emulation of guest syscalls.

>
>      buf = lock_user(VERIFY_WRITE, ptr, len, 0);
> -    ret = pread(fd, buf, len, offset);
> -    unlock_user(buf, ptr, len);
> +    if (buf) {
> +        ret = pread(fd, buf, len, offset);

A different bug, but if ret here indicates that pread()
failed we should be returning -errno.

> +        unlock_user(buf, ptr, len);
> +    }
>      return ret;
>  }

-- PMM